cheetah

27 Mar

cheetah

and cattle. The syndrome is named after the Cuban physician M. Che´diak and the Japanese pediatrician O. Higashi who described the condition in 1952 and 1954, respectively. See Aleutian mink. cheetah See Acinonyx jubatus. chelating agent a compound made up of hetero- cyclic rings that forms a chelate with metal ions. Heme (q.v.) is an example of an iron chelate. The porphyrin ring in chlorophyll (q.v.) forms a magne- sium chelate.

chelation the holding of a metal ion by two or more atoms of a chelating agent. Chelicerata a subphylum of arthropods containing the species that have no antennae and possess pin- cerlike chelicerae as the first pair of appendages. See classification. chemical bonds See disulfide linkage, electrostatic bond, glycosidic bonds, high-energy bond, hydrogen bond, hydrophobic bonding, ionic bond, peptide bond, phosphodiester, salt linkage, van der Waals forces. chemical elements listed alphabetically by their symbols. The biologically important elements are shown in boldface type. See periodic table.

Ac                                                        Actinium
Ag                                                        Silver
Al                                                        Aluminum
Am                                                        Americium
Ar                                                        Argon
As                                                        Arsenic
At                                                        Astatine
Au                                                        Gold
B                                                         Boron
Ba                                                        Barium
Be                                                        Beryllium
Bi                                                        Bismuth
Bk                                                        Berkelium
Br                                                        Bromine
C                                                         Carbon
Ca                                                        Calcium
Cd                                                        Cadmium
Ce                                                        Cerium
Cf                                                        Californium
Cl                                                        Chlorine
Cm                                                        Curium
Co                                                        Cobalt
Cr                                                        Chromium
Cs                                                        Cesium
Cu                                                        Copper
Dy                                                        Dysprosium

Er                                                        Erbium
Es                                                        Einsteinium
Eu                                                        Europium
F                                                         Fluorine
Fe                                                        Iron
Fm                                                        Fermium
Fr                                                        Francium
Ga                                                        Gallium
Gd                                                        Gadolinium
Ge                                                        Germanium
H                                                         Hydrogen
He                                                        Helium
Hf                                                        Hafnium
Hg                                                        Mercury
Ho                                                        Holmium
I                                                         Iodine
In                                                        Indium
Ir                                                        Iridium
K                                                         Potassium
Kr                                                        Krypton
La                                                        Lanthanum
Li                                                        Lithium
Lr                                                        Lawrencium
Lu                                                        Lutetium
Md                                                        Mendelevium
Mg                                                        Magnesium

Mn                                                        Manganese
Mo                                                        Molybdenum
N                                                         Nitrogen
Na                                                        Sodium
Nb                                                        Niobium
Nd                                                        Neodymium
Ne                                                        Neon
Ni                                                        Nickel
No                                                        Nobelium
Np                                                        Neptunium
O                                                         Oxygen
Os                                                        Osmium
P                                                         Phosphorus
Pa                                                        Protactinium
Pb                                                        Lead
Pd                                                        Palladium
Pm                                                        Promethium
Po                                                        Polonium
Pr                                                        Praseodymium
Pt                                                        Platinum
Pu                                                        Plutonium
Ra                                                        Radium
Rb                                                        Rubidium
Re                                                        Rhenium
Rh                                                        Rhodium
Rn                                                        Radon

Ru                                                        Ruthenium
S                                                         Sulfur
Sb                                                        Antimony
Sc                                                        Scandium
Se                                                        Selenium
Si                                                        Silicon
Sm                                                        Samarium
Sn                                                        Tin
Sr                                                        Strontium
Ta                                                        Tantalum
Tb                                                        Terbium
Tc                                                        Technetium
Te                                                        Tellurium
Th                                                        Thorium
Ti                                                        Titanium
Tl                                                        Thallium
Tm                                                        Thulium
U                                                         Uranium
V                                                         Vanadium
W  Tungsten
Xe                                                        Xenon
Y                                                         Yttrium
Yb                                                        Ytterbium
Zn                                                        Zinc
Zr                                                        Zirconium

chemiosmotic theory the concept that hydrogen ions are pumped across the inner mitochondrial membrane, or across the thylakoid membrane of chloroplasts, as a result of electrons passing through the electron transport chain (q.v.). The electrochem- ical gradient that results is the proton motive force (pmf). ATP synthase harnesses the pmf to make ATP See Appendix C, 1961, Mitchell; adenosine phosphate, mitochondrial proton transport. chemoautotrophy See autotroph, methanogens. chemokines a large family of structurally homolo- gous cytokines (q.v.), 8 to 10 kilodaltons (kDa) in size.

The name “chemokine” is a contraction of “che- motactic cytokine.” Chemokines share the ability to stimulate leukocytic movement (chemokinesis) and directed movement (chemotaxis), especially of in- flammatory cells to damaged or infected sites. Exam- ples of chemokines include interleukin-8 (IL-8) that attracts neutrophils, basophils, and eosinophils, and monocyte chemotactic protein-1 (MCP-1) that acts specifically only on monocytes. Chemokines are pro- duced by several types of cells, including activated mononuclear phagocytes, tissue cells (endothelium, fibroblasts), and megakaryocytes (which give rise to platelets that contain stored chemokine). chemolithoautotroph an autotroph that gets its energy from oxidation of inorganic substances in the

chi structure
absence of light. Many hyperthermophiles use inor- ganic electron donors and acceptors in their energy metabolism and obtain their carbon from CO2. See lithotroph, Methanococcus jannaschii. chemostat an apparatus allowing the continuous cultivation of bacterial populations in a constant, competitive environment. Bacteria compete for a limiting nutrient in the medium. The medium is slowly added to the culture, and used medium plus bacteria are siphoned off at the same rate.

The con- centration of the limiting nutrient in the fresh me- dium determines the density of the steady-state population, and the rate at which the medium is pumped into the chemostat determines the bacterial growth rate. In chemostat experiments, environ- mental variables can be changed, one by one, to as- certain how these affect natural selection, or the en- vironment can be held constant and the differential fitness of two mutations can be evaluated. chemotaxis the attraction or repulsion of cells or organisms toward or away from a diffusing sub- stance.

Also known as chemotropism. chemotherapy the treatment of a disease with drugs of known chemical composition that are spe- cifically toxic to the etiological microorganisms and do not harm the host. The term was coined by Paul Ehrlich, who also gave such drugs the nickname magic bullets. See Salvarsan. chemotrophs organisms whose energy is the result of endogenous, light-independent chemical reactions.

A chemotroph that obtains its energy by metaboliz- ing inorganic substrates is called a chemolithotroph, whereas one that metabolizes organic substrates is called a chemoorganotroph. Contrast with prototrophs. See autotrophs. chiasma (plural chiasmata) the cytological mani- festation of crossing over; the cross-shaped points of junction between nonsister chromatids first seen in diplotene tetrads. See Appendix C, 1909, Janssens; 1929, Darlington; crossing over, meiosis, recombina- tion nodules.

chiasma interference the more frequent (in the case of negative chiasma interference) or less fre- quent (in the case of positive interference) occur- rence of more than one chiasma in a bivalent seg- ment than expected by chance. chiasmata See chiasma. chiasmatype theory the theory that crossing over between nonsister chromatids results in chiasma for- mation. chicken See Gallus domesticus. chimera an individual composed of a mixture of genetically different cells. In plant chimeras, the mixture may involve cells of identical nuclear geno- types, but containing different plastid types.

In more recent definitions, chimeras are distinguished from mosaics (q.v.) by requiring that the genetically dif- ferent cells of chimeras be derived from genetically different zygotes. See also aggregation chimera, het- erologous chimera, mericlinal chimera, periclinal chi- mera, radiation chimera. chimpanzee See Pan. Chinchilla lanigera a rodent native to the Andes mountains of South America. It is bred on commer- cial ranches for its pelt, and many coat color mutants are available. Its haploid chromosome number is 32. CHIP-28 an abbreviation for CHannel-forming In- tegral Protein of 28 kDa relative molecular mass.

CHIP-28 was purified from the plasma membranes of human erythrocytes and later shown to form channels permeable to water. It was renamed aquap- orin1 (AQP1). chiral descriptive of any molecules that exist in two mirror-image versions (enantiomers, q.v.). Chironomus a genus of delicate, primitive, gnat- like flies that spend their larval stage in ponds and slow streams. Nuclei from various larval tissues con- tain giant polytene chromosomes.

The salivary gland chromosomes of C. thummi and C. tentans have been mapped, and the transcription processes going on in certain Balbiani rings (q.v.) have been studied extensively. See Appendix C, 1881, Balbiani; 1952, Beermann; 1960, Clever and Karlson; chromosomal puff. chi sequence an octomeric sequence in E.

coli DNA, occurring about once every 10 kilobases, act- ing as a “hotspot” for RecA-mediated genetic recom- bination. chi-square ( 2) test a statistical procedure that en- ables the investigator to determine how closely an experimentally obtained set of values fits a given theoretical expectation.

The relation between χ2 and probability is presented graphically on page 74. See Appendix C, 1900, Pearson; degrees of freedom. chi structure a structure resembling the Greek let- ter χ, formed by cleaving a dimeric circle with a re- striction endonuclease that cuts each DNA circle only once. The parental monomeric duplex DNA molecules remain connected by a region of hetero- duplex DNA at the point where crossing over oc-

Chi square ( 2) test and Student t test probability chart

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